WO2014122909A1

WO2014122909A1 - Light receiving device, optical space communication device, and optical space communication method

Info

Publication number: WO2014122909A1
Application number: PCT/JP2014/000541
Authority: WO
Inventors: 柳田　美穂; 孝史石川; 想西村; 青木　一彦; 賢司田上; 貴裕戸泉
Original assignee: 日本電気株式会社
Priority date: 2013-02-06
Filing date: 2014-02-03
Publication date: 2014-08-14
Also published as: JPWO2014122909A1

Abstract

[Problem] To provide a light receiving device, an optical space communication device, and an optical space communication method whereby the incidence of communication errors due to angle misalignment of an incident light beam are suppressed without increasing the size of an optical system, even when a light beam sent from a moving body is incident while being acquired and tracked. [Solution] A light receiving device (1) has a light condensing means (11) for condensing a received substantially plane-wave light beam, and an optical fiber (12) on which the light beam condensed by the light condensing means (11) is incident, and an incidence end (12c) of the optical fiber (12) is disposed in a position where the optical coupling efficiency of the light beam incident on a core (12a) of the optical fiber (12) is kept equal to or higher than a predetermined level in an allowable range for the incidence angle of the light beam and outside the range of the depth of focus of the light condensing means (11) in relation to the optical axis direction of the light condensing means (11).

Description

Light receiving device, optical space communication device, and optical space communication method

The present invention relates to a light receiving device, an optical space communication device, and an optical space communication method.

Information acquired by an observation device mounted on a mobile object such as a satellite or an aircraft is transmitted to, for example, the ground using some information transmission means. In recent years, the performance of observation equipment has increased, and the amount of information acquired has increased. For this reason, it has been proposed to use optical space communication capable of higher-speed communication instead of radio wave communication for the above-described information transmission means. In 2006, the optical satellite communication experimental satellite "Kirari" succeeded in the world for the first time in the space optical communication between satellites. In addition to high speed, optical space communication has advantages such as high secrecy due to high beam directivity and low interference between lines. Therefore, optical space communication plays a major role as a large-capacity information transmission means such as information transmission from satellite to ground, information transmission from aircraft to ground, and information transmission from satellite to aircraft, ships, vehicles, etc. Is expected.

However, some problems remain in optical space communications. When receiving a light beam transmitted from a moving body, the optical antenna that receives the light beam is driven to capture and track the light beam in order to reliably collect the received substantially plane wave light beam on the optical fiber. It is necessary to maintain this state with high accuracy. In this case, for example, movement of the moving body, posture change during flight of the aircraft, turbulent flow in the vicinity, atmospheric fluctuation, and the like are factors that hinder acquisition and tracking. In addition, the antenna directivity error, the control error of a fine capture tracking mechanism (FPM: Fine Pointing Mechanism) that causes the light beam to enter the optical fiber, and the like are factors that hinder capture tracking. Due to these factors, a deviation occurs between the center of the diameter of the incident light beam and the center of the core of the optical fiber, and the optical coupling efficiency fluctuates (decreases). The optical coupling efficiency is the ratio of the light beam incident on the optical fiber out of the light beam. When the optical coupling efficiency decreases, the frequency of occurrence of communication errors increases.

∙ There are two types of technologies for suppressing fluctuations in optical coupling efficiency: mechanical control and optical configuration. For example, Patent Document 1 below describes an optical system that suppresses fluctuations in optical coupling efficiency by mechanical control. In the optical system described in Patent Document 1, even when there is a possibility of causing a positional deviation in a direction perpendicular to the optical axis and a focus positional deviation in the optical axis direction depending on the incident condition of incident light, each deviation is quickly corrected. The stable optical coupling state is maintained.

Also, Patent Document 2 describes a spatial light receiver that suppresses fluctuations in optical coupling efficiency by an optical configuration. The spatial light receiving device described in Patent Document 2 includes a deflecting device that guides incident light in a certain direction even when there is a change in the incident direction within a certain range when the spatial light propagation signal is incident on the light receiving device. ing. The light emitted from the deflecting device is collected by the condensing device, enters the optical fiber, and is guided to the optical signal device as an optical signal.

Patent Document 3 describes an optical transmission module that suppresses fluctuations in optical power and prevents fluctuations in optical power in an optical transmission module. The optical transmission module described in Patent Document 3 includes a laser diode that emits laser light, a lens that collects the laser light, and a fiber ferrule that includes a fiber core that receives the laser light emitted from the lens. . Further, the optical transmission module described in Patent Document 3 includes the lens itself, a stop provided in front of the lens, or after the lens.

Patent Document 4 describes an optical coupling module in which a semiconductor laser, a condenser lens, and an optical fiber are integrated. In this optical coupling module, the incident end surface of the optical fiber is shifted to the front side surface or the rear side in the laser beam traveling direction with respect to the beam waist position of the laser beam emitted from the semiconductor laser and collected by the condenser lens. Yes.

Japanese Patent Laid-Open No. 2007-079387 JP 2008-233179A Japanese Patent No. 39507779 JP 09-318851 A

In the optical system described in Patent Document 1, tracking feedback control is performed to eliminate a positional deviation between the beam diameter center and the fiber core diameter center in a direction orthogonal to the optical axis using, for example, a galvano mirror. Furthermore, in the optical system described in Patent Document 1, focus feedback control for eliminating the focus position shift in the optical axis direction is performed. The positional deviation between the center of the beam diameter in the direction perpendicular to the optical axis and the center of the fiber core diameter is called a tracking error, and the focal positional deviation in the optical axis direction is called a focus error. At this time, in the focus feedback control, even if there is a tracking error, the focus error is detected by the focus position detection means without affecting the detection accuracy. The focus position detection means can keep the focus error within the depth of focus range and maintain an optimal focus state. However, when incident light that passes through the atmosphere while capturing and tracking a moving object is incident, the angle variation of the incident light is so severe that tracking errors are suppressed even if tracking feedback control is performed using a galvanometer mirror. It becomes difficult. Even if the processing and assembly accuracy of the optical module is increased, it is difficult to eliminate the tracking error to a level that does not cause a problem as the received light power fluctuation, and the fluctuation in the received light power remains even when the focus error is eliminated.

Also, for example, in the spatial light receiving device described in Patent Document 2, incident light having a different incident direction can be converted into light in a predetermined direction by making light incident on the optical fiber through the deflecting device. For this reason, even if the incident direction of incident light changes, the utilization efficiency of the received light can be improved. However, when a deflecting device is applied to an optical space communication device, the optical system becomes large and complicated.

If the processing accuracy of the normal optical module is sufficient, the deviation between the center of the aperture through which the light emitted from the fixed laser diode passes and the center of the lens should be sufficiently smaller than the allowable value in question. Can do. For this reason, for example, in the optical transmission module described in Patent Document 3, fluctuations in optical coupling efficiency can be suppressed. On the other hand, when the light source is not fixed, for example, consider the case of receiving light transmitted from a moving body and propagating light into the atmosphere. In this case, the deviation between the center of the incident light beam while capturing and tracking and the center of the lens focused on the fiber is much larger than the deviation between the center of the aperture and the center of the lens that can be achieved with the optical transmission module. Become. For this reason, when receiving the light transmitted from the moving body, the received light power fluctuates greatly even if a diaphragm is used as in this optical transmission module.

Also, in the optical coupling module described in Patent Document 4, the optical fiber output can be controlled to about 1 mW to 6 mW, for example, without changing the operating current of the semiconductor laser. This optical coupling module shifts the incident end face of the optical fiber forward or backward in the direction of travel of the beam with respect to the laser beam waist position in order to receive the laser beam with appropriate power. In addition, the optical coupling module tilts the central axis of the core of the optical fiber with respect to the propagation direction of the laser beam in order to receive the laser beam with an appropriate power. In this regard, Patent Document 4 describes the effects of optical fiber positional deviation and angular deviation with respect to a laser beam emitted from a semiconductor laser in order to receive light with an appropriate power, that is, to suppress the received light power. The calculated data is disclosed. However, from these data, it is impossible to take into account the influence and countermeasures due to the change in the incident angle of the light incident from the moving body. For example, regarding data relating to any of the correlations among the light beam emitted from the moving object, the tilt angle variation range due to the presence of atmospheric fluctuations, the position of the optical fiber, and the variation in optical coupling efficiency Patent Document 4 does not disclose anything. In an optical space communication device in which a light emitting element is not included in the constituent elements, it is difficult to determine the position of the optical fiber without taking into consideration the range of angular deviation and the amount of fluctuation in optical coupling efficiency.

The present invention has been made in view of the above circumstances, and suppresses the occurrence of communication errors without increasing the size of the optical system even when a light beam transmitted from a moving body is incident while being captured and tracked. An object of the present invention is to provide a light receiving device, an optical space communication device, and an optical space communication method.

The light-receiving device according to the first aspect of the present invention includes:
A light receiving device for receiving a substantially plane wave light beam,
Condensing means for condensing the received light beam;
An optical fiber for entering the light beam collected by the light collecting means,
The optical coupling efficiency of the light beam incident on the core of the optical fiber outside the range of the focal depth of the light collecting means with respect to the optical axis direction of the light collecting means and within the range where the incident angle of the light beam can be taken. The incident end of the optical fiber is disposed at a position where the optical fiber maintains a predetermined level or more.

An optical space communication device according to a second aspect of the present invention provides:
A light receiving device according to the first aspect of the present invention;
Control means for controlling the incident angle of the light beam incident on the light receiving device; and
The position of the incident end of the optical fiber is defined based on a possible range of the incident angle of the light beam with respect to the optical axis of the condensing means controlled by the control means.

An optical space communication method according to a third aspect of the present invention includes:
An optical space communication apparatus comprising: a light collecting unit that collects a substantially plane wave light beam; and an optical fiber that receives the light beam collected by the light collecting unit; and a light receiving device that receives the light beam. In the optical space communication method using
The optical coupling efficiency of the light beam incident on the core of the optical fiber outside the range of the focal depth of the light collecting means with respect to the optical axis direction of the light collecting means and within the range where the incident angle of the light beam can be taken. The incident end of the optical fiber is arranged at a position that maintains a predetermined level or more.

According to the present invention, since the incident end of the optical fiber is arranged outside the range of the focal depth of the light converging means, it is possible to reduce the amount of fluctuation in the received light power caused by the angular deviation of the light beam. For this reason, even when the light beam transmitted from the moving body is incident while being captured and tracked, it is possible to suppress the occurrence of a communication error due to the angular deviation of the incident light beam without increasing the size of the optical system.

It is a figure which shows the basic composition of the light-receiving device which concerns on the 1st Embodiment of this invention. It is explanatory drawing which shows angle deviation | shift amount (theta) and offset amount x. It is a characteristic graph which shows the relationship between angle shift | offset | difference amount (theta) and optical coupling efficiency. It is a characteristic graph which shows the relationship between angle shift | offset | difference amount (theta) and optical coupling efficiency in the light-receiving device which concerns on the 2nd Embodiment of this invention. It is a characteristic graph which shows the variation | change_quantity of optical coupling efficiency with respect to angle deviation | shift amount (theta) in the light-receiving device which concerns on the 3rd Embodiment of this invention, and angle deviation | shift amount (theta). It is a figure which shows the basic composition of the optical space communication apparatus which concerns on the 4th Embodiment of this invention. It is a figure which shows the basic composition of the light-receiving device which concerns on the 4th Embodiment of this invention. It is a characteristic graph which shows the relationship between angle shift | offset | difference amount (theta) and optical coupling efficiency in the light-receiving device which concerns on the 4th Embodiment of this invention. It is a characteristic graph which shows the relationship between angle shift | offset | difference amount (theta) and optical coupling efficiency in the light-receiving device which concerns on the 5th Embodiment of this invention.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent parts are denoted by the same reference numerals.
[First Embodiment]
First, a light receiving device according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram showing a basic configuration of a light receiving device according to the present embodiment. The light receiving device according to the present embodiment is a light receiving device that receives a light beam emitted from a communication partner. As shown in FIG. 1, the light receiving device 1 includes a condensing unit 11 and an optical fiber 12. The condensing unit 11 and the optical fiber 12 are positioned so that a light beam of a parallel light beam (substantially plane wave light beam) is incident in parallel to the optical axis.

The condensing means 11 condenses the received light beam. In FIG. 1, a state in which a light beam incident along the optical axis of the light collecting unit 11 from the left side is refracted in the light collecting unit 11 and condensed on the right side of the light collecting unit 11 is indicated by a dotted line. A light beam condensed by the condensing means 11 is incident on and guided to the optical fiber 12. For the condensing means 11, for example, a convex lens or a concave mirror is used. In the present embodiment, a case where a convex lens is used as the light collecting means 11 will be described.

The point where the light beam of the parallel light beam is refracted by the condensing means 11 and condensed on the optical axis becomes the focal point. When light emitted from a certain object is focused on the focal point through the condensing unit 11, a state where a clear image can be formed before and after the focal point in the optical axis direction of the condensing unit 11, that is, a state in focus. There is a range. The distance between the limits of this range is called the depth of focus.

The optical fiber 12 receives and propagates the light beam incident from the condensing means 11. The optical fiber 12 includes a core 12a and a clad 12b surrounding the core 12a. In the optical fiber 12, the light beam propagates through the core 12a. In the present embodiment, the incident end of the core 12 a is the incident end 12 c of the optical fiber 12.

In the light receiving device 1 having the above configuration, as shown in FIG. 1, the substantially plane wave light beam incident on the condensing means 11 is condensed and incident on the core 12 a from the incident end 12 c of the optical fiber 12. The optical fiber 12 guides the light beam condensed by the condensing means 11. The ratio of the light beam incident on the optical fiber 12 out of the light beam that has passed through the condensing means 11 is called optical coupling efficiency. The optical coupling efficiency at the maximum optical coupling efficiency is defined as 0 [dB].

Generally, the optical coupling efficiency is maximized under the following conditions. For example, consider a case where a light beam is incident on the light collecting means 11 at an angle parallel to the optical axis. In this case, by making the central axis of the optical fiber 12 (the central axis of the core 12a) coincide with the optical axis of the condensing means 11, the incident end 12c of the optical fiber 12 is coincident with the focal point of the condensing means 11. The optical coupling efficiency is maximized. For this reason, in a general light receiving device, the incident end of the optical fiber is arranged at the focal position.

Also, since the focal depth is within the same range as the focal point, the optical coupling efficiency is almost the maximum even within the focal depth range. In the present embodiment, the following description is given focusing on the point where the optical coupling efficiency is maximized, but the present invention is not limited to this.

However, even when the light collecting unit 11 is positioned so that the light beam incident on the light collecting unit 11 enters in parallel to the optical axis of the light collecting unit 11, the incident direction of the light beam may fluctuate. is there. The incidence of the light beam from the oblique direction with respect to the optical axis is called an angular deviation. As shown in FIG. 2, the incident angle of the light beam with respect to the optical axis of the condensing means 11 is defined here as an angle deviation amount θ. When the optical axis of the condensing means 11 and the incident angle of the light beam coincide with each other and there is no angular deviation, the angular deviation amount θ = 0 [deg].

The change of the optical coupling efficiency due to the angle shift will be described with reference to FIG. As shown in the figure, when a light beam is incident on the condensing means 11 from an oblique direction (broken line in the figure), the light beam is focused at a position deviating from the central axis of the optical fiber 12. As a result, a tracking error occurs, causing a reduction in optical coupling efficiency and a reduction in received light power.

In the light receiving device 1, the incident end 12c of the optical fiber 12 is shifted from the focal point in the optical axis direction (the direction away from the light collecting means 11). More specifically, the incident end 12c of the optical fiber 12 is out of the range of the focal depth of the condensing unit 11 with respect to the optical axis direction of the condensing unit 11 and is in a range where the incident angle of the light beam can be taken. It is arranged at a position where the optical coupling efficiency of the light beam incident on the core 12a of the fiber 12 maintains a predetermined level or more.

The relationship between the angle shift amount θ and the optical coupling efficiency in the light receiving device 1 according to the present embodiment, that is, the light receiving device 1 in which the incident end 12c of the optical fiber 12 is offset from the focal point will be described with reference to FIG. To do. FIG. 3 shows an example of a characteristic graph showing the relationship between the angle shift of the light receiving device and the optical coupling efficiency.

In FIG. 3, the solid line indicates the relationship between the angle deviation and the optical coupling efficiency in the case of a light receiving device in which the incident end of the optical fiber is not offset from the focal point (hereinafter, no offset). On the other hand, the relationship between the angle deviation and the optical coupling efficiency when the incident end 12c of the optical fiber 12 corresponding to the light receiving device 1 according to the present embodiment is offset (hereinafter referred to as offset) is indicated by a broken line. . As shown in the figure, in a state where there is no angular deviation (angle deviation amount θ = 0 [deg]), the optical coupling efficiency is high when there is no offset, and the light when there is an offset (the light receiving device 1 of the present embodiment). The coupling efficiency is low.

When the value of the angle deviation amount θ is changed (larger), the optical coupling efficiency is lowered with or without the offset. At this time, the fluctuation amount (decrease amount) of the optical coupling efficiency differs depending on whether or not there is an offset. The fluctuation amount of the optical coupling efficiency is large when there is no offset and small when there is an offset.

In other words, when there is no offset, the maximum optical coupling efficiency is obtained in a state where there is no angular deviation (angle deviation amount θ = 0 [deg]), but the optical coupling efficiency is greatly reduced due to the angular deviation. On the other hand, in the case where there is an offset, the optical coupling efficiency does not reach the maximum optical coupling efficiency in the state where there is no angular deviation, but the decrease in the optical coupling efficiency caused by the angular deviation is in a state where there is focus (when there is no offset) It is more gradual than the case where the angle deviation occurs.

In FIG. 3, the minimum level L of the optical coupling efficiency necessary for accurate signal reception is indicated by a one-dot chain line, and the limit value θ _{MAX of the} range that the incident angle of the light beam can take is indicated by the two-dot chain line. ing. As shown in FIG. 3, there is a region where the optical coupling efficiency with an offset is higher than the optical coupling efficiency without an offset within a range that the incident angle of the light beam can take. Within the possible range of the incident angle of the light beam, there is a region where the optical coupling efficiency without offset is at a minimum level L or less, but the optical coupling efficiency with an offset is kept at the minimum level L or more.

Thus, according to the light receiving device 1, the incident end 12c of the optical fiber 12 is outside the range of the focal depth of the condensing unit 11 with respect to the optical axis direction of the condensing unit 11, and the incident angle of the light beam is The optical coupling efficiency of the light beam incident on the core 12a of the optical fiber 12 is arranged at a position that maintains a predetermined level (for example, the minimum level L) or more within a possible range. For this reason, even when the angular deviation of the light beam occurs, high optical coupling efficiency can be obtained, and the amount of change in the optical coupling efficiency when the angular deviation occurs can be reduced. That is, high optical coupling efficiency can be maintained regardless of the angular deviation.
[Second Embodiment]
Next, a light receiving device according to a second embodiment will be described. In the light receiving device according to the present embodiment, the optical coupling efficiency is maximized when the incident angle of the light beam incident on the core of the optical fiber is 0 at the incident end of the optical fiber with respect to the optical axis direction of the condensing means. It is arranged at a position where the optical coupling efficiency is higher in at least a part of the possible range of the incident angle of the light beam than the position.

Since the light receiving device according to the present embodiment has the same configuration as the light receiving device 1 according to the first embodiment described above (see FIG. 1), the same reference numerals are given and description thereof is omitted. In the present embodiment, the position of the incident end 12c of the optical fiber 12, that is, the value of the offset amount x shown in FIG. 2 is calculated based on the relationship between the angle deviation amount θ and the optical coupling efficiency.

The offset amount x is the amount of movement when the optical fiber 12 is shifted in the optical axis direction with reference to the focal point, as shown in FIG. The offset amount x when the optical fiber 12 moves away from the light collecting means 11 is set to a positive value. On the other hand, the offset amount x when the optical fiber 12 moves so as to approach the condensing means 11 is set to a negative value. Note that the sign of the offset amount x may be set arbitrarily.

FIG. 4 shows a characteristic graph showing the relationship between the angle deviation amount θ and the optical coupling efficiency. In FIG. 4, the result of the offset amount x = 0 mm (no offset) is indicated by a solid line, the result of the offset amount x = 1 mm is indicated by a broken line, and the result of the offset amount x = 2 mm is indicated by a dotted line.

As shown in FIG. 4, in a state where there is no angular deviation (angle deviation amount θ = 0 [deg]), the optical coupling efficiency is highest when the offset amount x = 0, and optical coupling when the offset amount x = 1 mm. The efficiency is the next highest, and the optical coupling efficiency is the lowest when the offset amount x = 2 mm. That is, the optical coupling efficiency and the offset amount x are inversely proportional, and the optical coupling efficiency decreases as the offset amount x increases.

When the value of the angle deviation amount θ changes (increases), the optical coupling efficiency decreases in any of the offset amounts x = 0 mm, 1 mm, and 2 mm. The fluctuation amount (decrease amount) of the optical coupling efficiency at this time is different for each of the offset amounts x = 0 mm, 1 mm, and 2 mm. The fluctuation amount of the optical coupling efficiency is the largest when the offset amount x = 0 mm, the next largest when the offset amount x = 1 mm, and the smallest when the offset amount x = 2 mm.

In other words, when there is no offset (when the offset amount x = 0 mm), the maximum optical coupling efficiency is obtained when there is no angular deviation (angular deviation θ = 0 [deg]), but optical coupling occurs due to the angular deviation. Efficiency is greatly reduced. On the other hand, when there is an offset (when the offset amount x = 1 mm and 2 mm), the optical coupling efficiency does not reach the maximum optical coupling efficiency when there is no angular deviation (angular deviation amount θ = 0 [deg]). However, the decrease in optical coupling efficiency caused by the angle shift is more gradual than when the angle shift occurs in a focused state (when the offset amount x = 0 mm). As a result, as described above, when an angle deviation occurs (when the value of the angle deviation amount θ increases), when the position of the incident end 12c of the optical fiber 12 is offset with respect to the optical axis direction. The optical coupling efficiency is higher than the optical coupling efficiency when no offset is provided.

In FIG. 4, the minimum level of optical coupling efficiency necessary for accurate signal reception is indicated by a one-dot chain line, and levels L1 and L2 determined when the receiving device 1 belongs to different communication systems are shown. Yes. Further, in FIG. 4, the limit value θ _{max of the} range that the incident angle of the light beam can take is indicated by a two-dot chain line.

In the example shown in FIG. 4, when the minimum level of optical coupling efficiency is L1, the offset amount x is desirably 2.0 mm, and when the minimum level of optical coupling efficiency is L2, the offset amount x is 1. 0.0 mm is desirable.

In this way, by calculating the offset amount x based on the angle deviation amount θ and the optical coupling efficiency, the offset amount x that can reduce the fluctuation of the received light power even when the angle deviation occurs is calculated. Can do.
[Third Embodiment]
Next, a light receiving device according to a third embodiment will be described. In the light receiving device according to the present embodiment, the optical beam direction of the light collecting unit is greater than the position where the optical coupling efficiency is maximum when the incident angle of the light beam incident on the core of the optical fiber is 0 with respect to the optical axis direction of the condensing unit. The incident end of the optical fiber is arranged at a position where the fluctuation amount of the optical coupling efficiency becomes small within the range where the incident angle can be taken.

Since the light receiving device according to the present embodiment has the same configuration as the light receiving device 1 according to the first and second embodiments described above (see FIG. 1), the same reference numerals are given and description thereof is omitted. In the present embodiment, the position of the incident end 12c of the optical fiber 12, that is, the value of the offset amount x shown in FIG. 2 is calculated based on the relationship between the angle deviation amount θ and the variation amount of the optical coupling efficiency.

The relationship between the angle deviation amount θ and the amount of change in optical coupling efficiency with respect to the angle deviation amount θ will be described with reference to FIG. FIG. 5 shows an example of a characteristic graph showing the fluctuation amount of the optical coupling efficiency due to the angle shift. This figure shows the optical coupling efficiency when the angle deviation amount θ is changed with respect to the state where there is no angle deviation in each of the offset amounts x = 0 mm, 1 mm, and 2 mm (due to the occurrence of the angle deviation). The result of plotting the amount of variation is shown. As shown in FIG. 5, if the offset amount x is given, the fluctuation of the received light power can be reduced even when the angular deviation occurs.

Therefore, in the light receiving device 1, the range of the depth of focus of the condensing unit 11 with respect to the position where the optical coupling efficiency of the light beam incident on the core 12a of the optical fiber 12 is maximized with respect to the optical axis direction of the condensing unit 11. The incident end 12c of the optical fiber 12 is disposed at an outer position. Specifically, with respect to the optical axis direction of the condensing means 11, the light beam is more than the position (focal point) at which the optical coupling efficiency becomes maximum when the incident angle of the light beam incident on the core 12a of the optical fiber 12 is zero. The incident end 12c of the optical fiber 12 is disposed at a position where the fluctuation amount of the optical coupling efficiency becomes small within a range that the incident angle can take. For example, the offset amount x is calculated to be 1 mm in order to make the fluctuation amount of the optical coupling efficiency within 6 [dB] within the range of the angle shift (angle shift amount θ = 0.03 [deg]).

As described above, the value of the offset amount x is determined based on the amount of angular deviation θ and the amount of change in the optical coupling efficiency with respect to the amount of angular deviation θ, so that even if an angular deviation occurs, fluctuations in received light power Can be reduced.
[Fourth Embodiment]
Next, an optical space communication apparatus according to the fourth embodiment will be described. The space optical communication apparatus according to the present embodiment is a communication apparatus that performs space optical communication by transmitting and receiving a substantially plane wave light beam to and from a mobile communication apparatus that is a communication partner. As shown in FIG. 6, the optical space communication apparatus 100 includes a coarse capture tracking mechanism (CPM: Coarse Pointing Mechanism) 2, an optical antenna (Optical Antenna) 3, a fine capture tracking mechanism (FPM) 4, a beam. A splitter (Beam Splitter) 5, a coarse acquisition and tracking sensor (CAS) 6, a fine acquisition and tracking sensor (FPS) 7, a controller 8, and a light receiving device 1 'are provided.

The coarse acquisition and tracking mechanism 2 is a mechanism for acquiring and tracking a communication partner based on a light beam (dotted line in the figure) transmitted by the communication partner, and is used together with the coarse acquisition and tracking sensor 6. The coarse capturing and tracking mechanism 2 includes an opening (not shown) through which the light beam is incident, a biaxial gimbal (Gimbal) that drives the opening in a predetermined direction, and a light beam that is incident from the opening. And a mirror that reflects toward the screen.

A part of the light beam incident on the coarse acquisition and tracking mechanism 2 is guided to the coarse acquisition and tracking sensor 6 through the optical antenna 3, the fine acquisition and tracking mechanism 4, and the beam splitter 5 (51). The coarse acquisition and tracking sensor 6 detects the position of the communication partner and the distance from the communication partner. The coarse acquisition tracking mechanism 2 performs a process of adjusting the position and angle with the communication partner based on a control signal (broken line in the figure) generated by the control unit 8 based on the detection result of the coarse acquisition tracking sensor 6. . By this processing, the light beam is roughly captured and tracked.

The coarse acquisition and tracking mechanism 2 may further include a rotation angle sensor such as a resolver that detects the attitude of the biaxial gimbal, and may control the attitude of the biaxial gimbal by the output of those sensors.

The optical antenna 3 reduces the light beam emitted from the coarse capture and tracking mechanism 2 to a predetermined size. The optical antenna 3 is an optical system that guides the reduced light beam to the fine capture and tracking mechanism 4. The optical antenna 3 is configured by combining a lens, a mirror, and the like, for example.

The fine capture and tracking mechanism 4 is a mechanism that captures and tracks the light beam emitted by the communication partner, and is used together with the fine capture and tracking sensor 7. The fine capturing and tracking mechanism 4 includes a mirror, a holding unit that holds the mirror, and an electromagnetic driving unit that drives the mirror, which are not shown. The mirror reflects the incident light beam. The holding unit is configured by a resilient member such as a spring, for example. The electromagnetic drive unit is configured by various actuators such as a VCM (Voice Coil Motor), a piezoelectric element, a servo motor, and a linear motor.

Part of the light beam incident on the fine capture and tracking mechanism 4 is guided to the fine capture and tracking sensor 7 through the beam splitters 5 (51) and 5 (52). The fine capture tracking sensor 7 detects the incident angle of the light beam incident on the light receiving device 1 ′.

The fine capture tracking mechanism 4 efficiently introduces the light beam emitted by the communication partner into the light receiving device 1 ′ based on the control signal generated by the control unit 8 based on the detection result of the fine capture tracking sensor 7. A process for adjusting the position and angle is performed. For example, the fine acquisition and tracking mechanism 4 adjusts the incident angle of the light beam incident on the light receiving device 1 ′ by driving the mirror by the electromagnetic driving unit and changing the tilt of the mirror.

The fine capture and tracking mechanism 4 may further include an angle sensor such as an overcurrent sensor or an optical sensor that measures the tilt of the mirror. In this case, the angle of the mirror is controlled based on the output of the angle sensor.

The beam splitter 5 is an optical component in which two right angle prisms are bonded together and a dielectric multilayer film or a metal film is applied to the joint surface. The beam splitter 5 reflects a part of the incident light beam and transmits a part thereof. In this embodiment, a beam splitter in which two right-angle prisms are bonded together is adopted. However, the present invention is not limited to this. For example, a plate-type beam splitter may be adopted.

The optical space communication apparatus 100 according to the present embodiment includes a beam splitter 51 and a beam splitter 52 as the beam splitter 5. The beam splitter 51 branches the light beam that has passed through the fine capture and tracking mechanism 4 into a light beam that travels toward the coarse capture and tracking sensor 6 and a light beam that travels toward the light receiving device 1. The beam splitter 52 branches the light beam that has passed through the fine capture and tracking mechanism 4 to the fine capture and tracking sensor 7 and the light receiving device 1 '.

The coarse acquisition and tracking sensor 6 is a position sensor that detects the position of the communication partner based on the received light beam. The coarse acquisition and tracking sensor 6 detects the posture information of the communication partner based on the position of the light beam in the plane irradiated on the receiving surface. The attitude information of the communication partner detected by the coarse acquisition and tracking sensor 6 is transmitted to the control unit 8. For example, a quadrant PD (Photodiode) sensor, a PD sensor array, or the like can be employed as the coarse acquisition tracking sensor 6. In addition, a CMOS (Complementary Metal Oxide Semiconductor) image sensor, a CCD (Charge Coupled Device) image sensor, or the like can be employed.

The fine capture tracking sensor 7 detects the incident angle of the light beam incident on the light receiving device 1 ′ based on the received light beam. Information on the incident angle of the light beam detected by the fine capture tracking sensor 7 is transmitted to the control unit 8. As the fine capture tracking sensor 7, for example, a quadrant PD sensor, a PD sensor array, a CMOS image sensor, a CCD image sensor, or the like can be used in the same manner as the coarse capture tracking sensor 6.

The control unit 8 generates a control signal for causing the space optical communication apparatus 100 to perform space optical communication and a control signal for performing acquisition and tracking processing. For example, the control unit 8 generates a control signal for driving the biaxial gimbal of the coarse acquisition tracking mechanism 2 based on the posture information detected by the coarse acquisition tracking sensor 6 and the resolver of the coarse acquisition tracking mechanism 2 and also fine acquisition. A control signal for driving the VCM of the tracking sensor 7 is generated.

The light receiving device 1 'receives the light beam emitted by the communication partner and performs optical space communication (reception of transmission information) in the same manner as the light receiving device 1 according to the first to third embodiments described above. As shown in FIG. 7, the light receiving device 1 ′ includes a condensing unit 11, an optical fiber 12, a photoelectric conversion element 13, and a housing 14 that houses these components.

The photoelectric conversion element 13 is an element that converts a light beam into an electrical signal. For example, a photodiode can be used as the photoelectric conversion element 13. The photoelectric conversion element 13 outputs an electrical signal having an output value corresponding to the amount of light beam guided by the optical fiber 12.

In the light receiving device 1 ′ having the above-described configuration, the condensing unit 11 condenses the incident substantially plane wave light beam. The optical fiber 12 guides the light beam condensed by the condensing unit 11. The photoelectric conversion element 13 converts transmission information included in the light beam guided by the optical fiber 12 into an electrical signal.

Further, in the light receiving device 1 ′, the incident end 12 c of the optical fiber 12 has an offset as in the light receiving device 1 described above. Specifically, the light beam with respect to the optical axis of the condensing means 11 controlled by the control means comprising the coarse acquisition tracking mechanism 2, the fine acquisition tracking mechanism 4, the coarse acquisition tracking sensor 6, the fine acquisition tracking sensor 7, and the controller 8. The position of the incident end 12c of the optical fiber 12 is defined based on the possible range of the incident angle. Therefore, in the light receiving device 1 ′, even when the angle deviation of the light beam occurs due to the control error of the control means, the decrease in the optical coupling efficiency is suppressed and the optical coupling efficiency is kept high.

In the optical space communication apparatus 100 according to the present embodiment, the optical beam and the control unit are used to regulate the light beam incident on the light receiving unit 1 ′. However, when the communication partner is a moving body, the control unit When the above control error occurs, the light beam may enter the light receiving device 1 ′ in an oblique direction. Therefore, in the light receiving device 1 ′, the incident end 12 c of the optical fiber 12 is disposed outside the range of the focal depth of the light collecting unit 11. That is, the incident end 12c of the optical fiber 12 is disposed at a position calculated based on a possible range of the incident angle of the light beam with respect to the optical axis of the condensing unit 11 controlled by the control unit. Thereby, even if the angle deviation of a light beam arises, the fluctuation | variation of optical coupling efficiency can be suppressed.

In this way, by calculating the offset amount x based on the angle deviation amount θ and the optical coupling efficiency, the condensing unit 11 controlled by the control unit that controls the incident angle of the light beam incident on the light receiving device 1 ′. The position of the incident end 12c of the optical fiber 12 is defined based on the possible range of the incident angle of the light beam with respect to the optical axis. Specifically, with respect to the optical axis direction of the condensing means 11, the incident angle of the light beam is greater than the position where the optical coupling efficiency is maximized when the incident angle of the light beam incident on the core 12a of the optical fiber 12 is zero. The incident end 12c of the optical fiber 12 is disposed at a position where the optical coupling efficiency is high in at least a part of the possible range. In other words, the offset amount x can be calculated based on the fluctuation amount of the optical coupling efficiency, the control accuracy of the coarse acquisition tracking system, the control accuracy of the fine acquisition tracking system, and the like.

For example, as shown in FIG. 8, when the maximum value of the angle shift amount θ obtained according to the control accuracy of the coarse acquisition tracking system or the control accuracy of the fine acquisition tracking system is θ1 _MAX , The quantity x is preferably 2 mm. However, when the maximum value of the angle shift amount θ obtained in accordance with the control accuracy of the coarse acquisition tracking system or the control accuracy of the fine acquisition tracking system is θ2 _MAX , the offset amount x is 1 mm. Is desirable.
[Fifth Embodiment]
Next, an optical space communication apparatus according to the fifth embodiment will be described. The space optical communication apparatus according to the present embodiment defines the position of the incident end 12c of the optical fiber 12 based on the optical coupling efficiency or the variation amount of the optical coupling efficiency allowed by the communication system that transmits and receives the light beam. is there.

The space optical communication apparatus according to the present embodiment has the same configuration as that of the space optical communication apparatus 100 (see FIG. 6) described above, and the same reference numerals are given and description thereof is omitted. In the present embodiment, in the light receiving device 1 ′, the incident end 12 c of the optical fiber 12 is arranged at a position having an offset from the focal point in the optical axis direction. Thereby, even when the communication state with the communication partner deteriorates, that is, when the communication partner is a mobile body, or when a control error of the coarse acquisition tracking mechanism 2 or the fine acquisition tracking mechanism 4 occurs, the predetermined level or more is exceeded. The optical coupling efficiency is maintained.

As described above, the offset amount x can be calculated based on the relationship between the received light power or the error rate of the communication system and the angular deviation. For example, as shown in FIG. 9, when the optical coupling efficiency allowed by the communication system is high and the minimum level is L81 or more, the offset amount x is desirably 2 mm. When the minimum level required for the optical coupling efficiency is L82 or more, the offset amount x may be 1 mm.

In addition, although the optical space communication apparatus 100 of this embodiment receives the light beam by the rough acquisition tracking mechanism 2 and is incident on the optical antenna 3, the optical space communication apparatus 100 drives the optical antenna 3 with a biaxial gimbal. However, the moving body may be captured and tracked, and the light beam may be guided to the fine capture and tracking mechanism 4.

Alternatively, the coarse acquisition tracking sensor 6 may be placed not at the fine acquisition tracking mechanism 4 but at the position where the light beam immediately after the coarse acquisition tracking mechanism 2 is separated by the beam splitter 5.

Further, in the above embodiment, the case where communication with a mobile unit is described. However, the present invention is not limited to this. For example, the present invention may be applied to communication between optical space communication devices 100 that are attached to a fixed structure such as an outdoor building but may vibrate due to wind or the like.

In addition, the characteristic graph demonstrated in the said embodiment was calculated | required by the optical simulation using the method of the said nonpatent literature 1. FIG. Specifically, this optical simulation was performed using the following conditions.

Wavelength of light beam: 1.55 μm
Diameter of the core 12a of the optical fiber 12: 30 μm
Focal length: 56mm
Rayleigh length: 0.46mm
The Rayleigh length is a depth of focus when incident light is regarded as a Gaussian beam.

The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

Part or all of the above-described embodiment can be described as in the following supplementary notes, but is not limited thereto.
(Appendix 1)
A light receiving device for receiving a substantially plane wave light beam,
Condensing means for condensing the received light beam;
An optical fiber for entering the light beam collected by the light collecting means,
The optical coupling efficiency of the light beam incident on the core of the optical fiber outside the range of the focal depth of the light collecting means with respect to the optical axis direction of the light collecting means and within the range where the incident angle of the light beam can be taken. A light receiving device in which an incident end of the optical fiber is disposed at a position where the optical fiber maintains a predetermined level or more.
(Appendix 2)
With respect to the optical axis direction of the condensing means, the range in which the incident angle of the light beam can take more than the position where the optical coupling efficiency is maximized when the incident angle of the light beam incident on the core of the optical fiber is 0 The light receiving device according to supplementary note 1, wherein an incident end of the optical fiber is disposed at a position where at least part of the optical coupling efficiency is high.
(Appendix 3)
With respect to the optical axis direction of the condensing means, the range in which the incident angle of the light beam can take more than the position where the optical coupling efficiency is maximized when the incident angle of the light beam incident on the core of the optical fiber is 0 The light receiving device according to supplementary note 1, wherein an incident end of the optical fiber is disposed at a position where the fluctuation amount of the optical coupling efficiency becomes small.
(Appendix 4)
The light receiving device according to any one of appendices 1 to 3, and
Control means for controlling the incident angle of the light beam incident on the light receiving device; and
An optical space communication apparatus in which the position of the incident end of the optical fiber is defined based on a possible range of the incident angle of the light beam with respect to the optical axis of the condensing means controlled by the control means.
(Appendix 5)
The optical space communication apparatus according to appendix 4, wherein a position of an incident end of the optical fiber is defined based on the optical coupling efficiency allowed by a communication system that transmits and receives the light beam or a variation amount of the optical coupling efficiency.
(Appendix 6)
An optical space communication apparatus comprising: a light collecting unit that collects a substantially plane wave light beam; and an optical fiber that receives the light beam collected by the light collecting unit; and a light receiving device that receives the light beam. In the optical space communication method using
The optical coupling efficiency of the light beam incident on the core of the optical fiber outside the range of the focal depth of the light collecting means with respect to the optical axis direction of the light collecting means and within the range where the incident angle of the light beam can be taken. An optical space communication method in which the incident end of the optical fiber is disposed at a position where the optical fiber maintains a predetermined level or more.

This application claims priority based on Japanese Patent Application No. 2013-021739 filed on Feb. 6, 2013, the entire disclosure of which is incorporated herein.

1, 1 'Light receiving device 11 Condensing means 12 Optical fiber 12a Core 12b Cladding 12c Incident end 13 of optical fiber Photoelectric conversion element 14 Housing 2 Coarse capture tracking mechanism (CPM)
3 Optical antenna 4 Fine capture and tracking mechanism (FPM)
5, 51, 52 Beam splitter 6 Coarse acquisition tracking sensor (CAS)
7 Fine capture and tracking sensor (FPS)
8 Control unit 100 Optical space communication device x Offset amount θ Angle deviation amount

Claims

A light receiving device for receiving a substantially plane wave light beam,
Condensing means for condensing the received light beam;
An optical fiber for entering the light beam collected by the light collecting means,
The optical coupling efficiency of the light beam incident on the core of the optical fiber outside the range of the focal depth of the light collecting means with respect to the optical axis direction of the light collecting means and within the range where the incident angle of the light beam can be taken. A light receiving device in which an incident end of the optical fiber is disposed at a position where the optical fiber maintains a predetermined level or more.
With respect to the optical axis direction of the condensing means, the range in which the incident angle of the light beam can take more than the position where the optical coupling efficiency is maximized when the incident angle of the light beam incident on the core of the optical fiber is 0 The light receiving device according to claim 1, wherein an incident end of the optical fiber is disposed at a position where at least part of the optical coupling efficiency is high.
With respect to the optical axis direction of the condensing means, the range in which the incident angle of the light beam can take more than the position where the optical coupling efficiency is maximized when the incident angle of the light beam incident on the core of the optical fiber is 0 The light receiving device according to claim 1, wherein an incident end of the optical fiber is disposed at a position where the fluctuation amount of the optical coupling efficiency becomes small.
The light receiving device according to any one of claims 1 to 3,
Control means for controlling the incident angle of the light beam incident on the light receiving device,
An optical space communication apparatus in which the position of the incident end of the optical fiber is defined based on a possible range of the incident angle of the light beam with respect to the optical axis of the condensing means controlled by the control means.
5. The optical space communication device according to claim 4, wherein a position of an incident end of the optical fiber is defined based on the optical coupling efficiency allowed by the communication system that transmits and receives the light beam or a variation amount of the optical coupling efficiency. .
An optical space communication apparatus comprising: a light collecting unit that collects a substantially plane wave light beam; and an optical fiber that receives the light beam collected by the light collecting unit; and a light receiving device that receives the light beam. In the optical space communication method using
The optical coupling efficiency of the light beam incident on the core of the optical fiber outside the range of the focal depth of the light collecting means with respect to the optical axis direction of the light collecting means and within the range where the incident angle of the light beam can be taken. An optical space communication method in which the incident end of the optical fiber is disposed at a position where the optical fiber maintains a predetermined level or more.